1. Field of the Invention
The present invention relates to an image forming apparatus for use as a copying machine or a laser printer, and more particularly to a small-sized and inexpensive image forming apparatus suitable for personal use.
2. Description of Related Art
FIG. 1 shows a typical image forming system which is provided with a drum photoconductor and is adapted to conventional copying machines and laser printers. In U.S. Pat. No. 4,696,562, there is disclosed an apparatus which is provided with an endless belt photoconductor.
In the apparatus shown in the FIG. 1, there are disposed an exposure optical system b above a photoconductive drum a and a transfer charger c and the like under the photoconductive drum a respectively. Around the photoconductive drum a, there are also arranged a developing unit d, cleaner e, eraser f and charger g with a space h for exposure. The diameter of the photoconductive drum a is set as small as possible (for instance, about 30 mm) in order to be able to accommodate necessary devices around the photoconductive drum a. A transport path i for transporting a transfer material is formed between the photoconductive drum a and the transfer charger c which is disposed under the drum, and a fixing unit j is arranged at the end of the path i.
In the apparatus disclosed in the U.S. Patent, various devices necessary for image forming operation are disposed around the endless belt photoconductive drum similarly to the conventional apparatus as illustrated in the FIG. 1. The apparatus is provided with an exposure section for carrying out copying operations and a laser print head so that it can be used either in copying machines or printers.
The copying machine shown in the FIG. 1 is designed to make it's size smaller and thinner by making the diameter of the photoconductive drum a as small as possible. However, there is a limit in making the size smaller since sufficient space is required for arranging various image forming devices including the exposure optical system b around the photoconductive drum a. On the contrary, it become rather bulky since various devices required for image forming operation are collectively disposed around the photoconductive drum a. Moreover, the fixing unit j becomes more bulky downward than those image forming devices since it is arranged in the transfer material transporting path i on the same level of the transfer section. Under the circumstances, copying machines have not been manufactured sufficiently thinner yet.
In order to reduce the number of image forming devices, it may be considered to properly use one charger as a charging device and a transfer device during two rounds of rotations of the photoconductive drum a. Even in this case, however, the diameter of the drum a becomes about 100 mm when JIS A4 size sheet is used since sufficient peripheral length of the photoconductive drum a is required for practicable copying operation, which eventually makes the size of the copying machine more larger.
In the apparatus disclosed in the U.S. Patent, on the other hand, image forming devices may be arranged without increasing the size in the upper and lower portions since the belt-shaped photoconductor is stretched crossways. However, there is not specific consideration which is given to the arrangement of the image forming devices and fixing device, and therefore, the machine can not be manufactured small and thin. Especially, when exposure section for copying operation and a laser beam print head are provided together for use both copying machines and printers as the one disclosed in the U.S. Patent, the machine becomes totally large in size.
With recent popularization of word processors, personal computers and the like for personal use, a small-sized and inexpensive copying machine which can also be used as a printer is desired. However, such a convenient machine has not been introduced yet because of the reasons as described above.